It is well known that sea waves appear to constitute a nearly unlimited resource of energy which, if exploited efficiently, may possibly solve a significant proportion of the world's energy problems. However, despite of many attempts to exploit sea-wave energy, no commercially successful system for converting sea wave energy into electrical power has been devised so far.
In general, three different types of wave power apparatuses have been proposed in the prior art. One such apparatus is disclosed in U.S. Pat. No. 6,476,511, the apparatus comprising a plurality of buoyant cylindrical body members connected together at their ends to form an articulated chain-like structure. Each pair of adjacent cylindrical members is connected to each other by a coupling member, which permits relative rotational movement of the cylindrical members about a transverse axis. Adjacent coupling members may permit relative rotation about mutually orthogonal transverse axes. Each coupling member is provided with elements, such as a set of hydraulic rams, which resist and extract power from the relative rotational movement of the body members. The apparatus floats freely in the sea surface and is moored to the sea floor.
A second type of wave power apparatus comprises one or more surface floats capable of moving along the surface of the sea under the action of waves, and a reference member, which is fully submerged in the sea at a certain depth, and which is substantially unaffected by the waves, cf. for example U.S. Pat. No. 4,453,894. The movement of the float in the surface of the sea causes the displacement of a hydraulic fluid in a hydraulic system comprising hydraulic devices which interconnect the surface float or floats and the reference member, whereby useful energy may be extracted from the hydraulic system. It will be appreciated that this apparatus is also moored to the sea floor.
Finally, a third type of wave power apparatus is one having one or more arms supported by a supporting structure carrying one or more floats which are caused to move by the waves. The energy of moving waves transmitted into the arms and may be conveyed into a hydraulic system, as in the system of U.S. Pat. No. 4,013,382, or into a mechanical system of shafts which, via a mechanical transmission system, drive one or more electric generators for the production of electricity, as in the system of WO 01/92644.
The present invention is generally concerned with the third type of wave power apparatuses mentioned above. It is an object of preferred embodiments of the invention to provide an apparatus, which allows for an even power output of power conversion means of the apparatus, i.e. a power output which is substantially constant over time. It is a further object of preferred embodiments to provide a system which reduces or eliminates the need for frequency converters. It is a further object of preferred embodiments to provide a wave power apparatus which may conveniently be taken out of operation, e.g. to prevent formation of ice on various parts of the apparatus during operation. It is a still further object of preferred embodiments of the invention to provide an apparatus, which allows for convenient maintenance access to arms and floats, most preferably to allow for maintenance access of individual arms and floats in systems comprising a plurality of arms, each provided with a float. It is a still further object of preferred embodiments to provide an apparatus which may conveniently be conveyed from an on-shore production facility to the operational site at the open sea.